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| United States Patent |
6,100,361
|
|
Keller
|
August 8, 2000
|
Golf ball top coating containing an aromatic/aliphatic polyisocyanate
copolymer
Abstract
A urethane top coat prepared by combining a polyol and a blend of an
aliphatic diisocyanate and an aliphatic/aromatic polyisocyanate copolymer
is provided, along with a method for its use as the top coating for a golf
ball. The inventive top coating demonstrates an increased rate of curing
compared to other top coatings having similar abrasion resistance and
color retention qualities.
| Inventors:
|
Keller; Viktor (Enfield, CT)
|
| Assignee:
|
Spalding Sports Worldwide, Inc. (Chicopee, MA)
|
| Appl. No.:
|
302891 |
| Filed:
|
April 30, 1999 |
| Current U.S. Class: |
528/67; 528/44; 528/59; 528/60; 528/65; 528/66 |
| Intern'l Class: |
C08G 018/70 |
| Field of Search: |
528/44,59,60,65,66,67
|
References Cited
U.S. Patent Documents
| 4359550 | Nov., 1982 | Narayan et al. | 524/871.
|
| 4518761 | May., 1985 | Richter et al. | 528/67.
|
| 5344851 | Sep., 1994 | Hovestadt et al. | 521/49.
|
| 5409233 | Apr., 1995 | Kennedy | 273/235.
|
| 5459220 | Oct., 1995 | Kennedy | 528/44.
|
| 5494291 | Feb., 1996 | Kennedy | 273/235.
|
| 5563207 | Oct., 1996 | Brahm et al. | 524/391.
|
| 5587448 | Dec., 1996 | Engen | 528/55.
|
| 5645931 | Jul., 1997 | Fan et al. | 428/334.
|
| Foreign Patent Documents |
| 1234972 | Jun., 1971 | GB.
| |
Other References
Product Information, Coatings, Miles, Industrial Chemicals Division, 1 page
(date unknown).
|
Primary Examiner: Woodward; Ana
Claims
What is claimed is:
1. A two-part polyurethane top coat, comprising:
a first part comprising a polyol; and
a second part comprising
(a) an aliphatic diisocyanate; and
(b) an aliphatic/aromatic polyisocyanate copolymer;
wherein said aliphatic/aromatic polyisocyanate copolymer is present in said
second part in a sufficient amount to accelerate curing of said top coat
and wherein said amount is less than 50 parts by weight per 50 parts by
weight of the aliphatic diisocyanate.
2. A polyurethane top coat, comprising the reaction product of:
a first part comprising a polyol; and
a second part comprising
(a) an aliphatic diisocyanate; and
(b) an aliphatic/aromatic polyisocyanate copolymer;
wherein said aliphatic/aromatic polyisocyanate copolymer is present in said
second part in a sufficient amount to accelerate curing of said top coat
and wherein said amount is less than 50 parts by weight per 50 parts by
weight of the aliphatic diisocyanate.
3. The polyurethane top coat as in claim 2, wherein said aliphatic
diisocyanate is selected from the group consisting of a biuret of
hexamethylene diisocyanate, an isocyanurate trimer of hexamethylene
diisocyanate, and mixtures thereof.
4. The polyurethane top coat as in claim 2, wherein said aliphatic/aromatic
polyisocyanate copolymer is comprised of toluene diisocyanate and
hexamethylene diisocyanate.
5. The polyurethane top coat as in claim 2, wherein said first part further
comprises a catalyst, wherein said catalyst is in said top coat at greater
than about 0.17 percent by weight solids in the top coat.
6. The polyurethane top coat as in claim 2, wherein said aliphatic/aromatic
polyisocyanate copolymer is present in said second part at up to 30 parts
by weight per 70 parts by weight of the aliphatic diisocyanate.
7. The polyurethane top coat as in claim 2, wherein said aliphatic/aromatic
polyisocyanate copolymer is present in said second part at up to 20 parts
by weight per 80 parts by weight of the aliphatic diisocyanate.
8. The polyurethane top coat as in claim 2, wherein said aliphatic/aromatic
polyisocyanate copolymer is present in said second part at up to 10 parts
by weight per 90 parts by weight of the aliphatic diisocyanate.
9. A polyurethane top coat, comprising:
a polyol;
an aliphatic diisocyanate; and
an aliphatic/aromatic polyisocyanate copolymer;
wherein said aliphatic/aromatic polyisocyanate copolymer is present in said
top coat in a sufficient amount to accelerate curing of said top coat and
wherein said amount is less than 50 parts by weight per 50 parts by weight
of the aliphatic diisocyanate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
The present invention relates to golf balls having a clear finish or top
coating and, in particular, to an improved polyurethane top coating
composition for golf balls.
For decades, golf balls were finished by applying an opaque coating to the
outer surface to the golf ball cover. To achieve a desirable white
appearance, a multicoat paint system typically comprising a primer coat
followed by one or more opaque coatings was applied to the golf ball. Such
golf balls are typically referred to as "painted balls".
In the 1980's, a pigment was incorporated into the cover material prior to
molding the cover of the golf ball, thereby eliminating the step of
painting the golf ball. Such golf balls are typically referred to as
"pigmented balls".
Whether the golf balls are painted or pigmented, identifying indicia such
as the manufacturer's trademark or logo, or a model or identification
number are stamped on the ball. In order to prevent the stamped indicia
from being rubbed off, and also to impart a desirable glossiness to the
ball, one or two clear finishes or top coatings are applied to the ball.
Typically, such clear coatings consist of a clear epoxy primer, followed
by a clear urethane top coat. The urethane top coat is usually a two part
polyurethane, including a polyol part and a diisocyanate part. The two
parts are mixed together and reacted to form the urethane coating.
While early urethane top coatings imparted a desirable glossiness to the
ball, they suffered from certain disadvantages. For example, the urethane
coatings made from aromatic diisocyanates tended to yellow very quickly
upon exposure to ultraviolet light, thus detracting from the appearance of
the painted or pigmented ball. Also, the early urethane coatings typically
suffered from adhesion and abrasion resistance problems. Good adhesion is
required to protect the indicia stamped on the ball, while good abrasion
resistance is needed to maintain the glossiness of the ball.
To avoid the problems associated with the early urethane top coatings,
urethane top coatings have been prepared using biurets and isocyanurate
trimers of hexamethylene diisocyanate as crosslinking agents. Coatings
made with such crosslinking agents exhibit superior adhesion and abrasion
resistance, and superior color retention upon exposure to ultraviolet
radiation. Top coatings using these crosslinking agents are disclosed in
U.S. Pat. No. 5,459,220, which is incorporated herein by reference in its
entirety.
Although the top coatings disclosed in U.S. Pat. No. 5,459,220 are
qualitatively superior to earlier top coatings, application of these and
other similar coatings to golf balls requires a drying or curing period.
To describe the typical application process in more detail, the polyol and
diisocyanate parts of the top coat are premixed in a pressure pot. Dry air
is used to push the coating to an air atomizing spray gun where it is
forced out of a small diameter fluid nozzle onto the surface of the golf
balls. The sprayed golf balls are then placed into an oven for a
predetermined length of time, and at a predetermined temperature, such
that the solvent evaporates and the polyol and the diisocyanate polymerize
to form the desired top coat. The oven times necessary to cure existing
top coats can range anywhere from five minutes to six hours or more, while
oven temperatures typically range from 140.degree. F. to 200.degree. F.
Regardless of whether the manufacturer uses a fast cure top coat (with cure
times measured in minutes) or a slow cure top coat (with cure times
measured in hours), the balls must spend some time in an oven to effect
the cure. As the time necessary to cure a particular top coat increases,
the golf balls must either spend more time in the ovens or be subjected to
higher oven temperatures. Either way, greater amounts of energy must be
applied to the golf balls to complete the manufacturing process, thus
increasing the cost of manufacture. In addition, as a golf ball is exposed
to greater amounts of heat, the possibility of damage to the surface of
the ball itself is increased. For example, the surface of a modern golf
ball is covered with spaced "dimples" to improve the aerodynamics of the
ball when it travels through the air. Excessive heat exposure may cause
the dimples to deform. Even a slight aberration in the shape of the
dimples can adversely affect the ball's aerodynamic properties.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a urethane
top coating that demonstrates an increased rate of curing compared to at
least some other top coatings.
Another object of the present invention is to provide a urethane top
coating that can be applied to a golf ball with less risk of damaging the
surface of the golf ball.
An additional object of the present invention is to provide a urethane top
coating that demonstrates superior adhesion and abrasion resistance and
yet still demonstrates an increased rate of curing compared to at least
some other top coatings.
Still another object of the present invention is to provide a urethane top
coating that demonstrates good color retention (non-yellowing) properties
and yet still demonstrates an increased rate of curing compared to at
least some other top coatings.
Other objects of the invention will become apparent to one skilled in the
art who has the benefit of the specification and the prior art.
One aspect of the invention which satisfies one or more of the foregoing
objects, in whole or in part, is a urethane top coat made from the
reaction of a polyol portion with an isocyanate blend comprised of an
aliphatic diisocyanate and an aliphatic/aromatic polyisocyanate copolymer,
where the aliphatic/aromatic copolymer is in the blend at up to 50 parts
by weight per 50 parts by weight of the purely aliphatic diisocyanate.
Another aspect of the invention is a urethane top coat as previously
defined, where the aliphatic diisocyanate is a biuret of hexamethylene
diisocyanate, an isocyanurate trimer of hexamethylene diisocyanate, or a
mixture of the two.
Still another aspect of the invention is a urethane top coat as previously
defined, where the aliphatic/aromatic polyisocyanate copolymer includes
toluene diisocyanate and hexamethylene diisocyanate.
Yet another aspect of the invention is a urethane top coat as previously
defined, where the polyol portion includes a catalyst that is present at
greater than about 0.17 percent by weight solids in the entire top coat.
As used herein, the phrase "weight solids" means the weight of the
substance or composition in question minus the weight of any solvents
present (such as methyl isobutyl ketone, methyl amyl ketone, or n-butyl
acetate).
Still another aspect of the invention is a method of coating a golf ball by
applying a urethane top coat as previously defined to the surface of the
golf ball.
Another aspect of the invention is a golf ball having a cover that is
coated with a urethane top coat as previously defined.
DETAILED DESCRIPTION OF THE INVENTION
The polyurethane top coat of the present invention is a two-part solvent
borne polyurethane system. The first part comprises a hydroxyl functional
polyol having an hydroxyl equivalent weight in the range of 50 to 1500,
with the preferred equivalent weight being 200 to 500. Compounds
containing the hydroxyl functional polyol contemplated herein include
polyesters, polyethers, or acrylics. Alternately, the hydroxyl functional
polyol is ethylenically saturated. Suitable saturated polyesters for use
herein include poly (oxydiethylene adipates) that are condensation
products of diethylene glycol and adipic acid, branched with
trimethylolpropane or pentaerythritol, and polycaprolactone
(hydroxycaproic acid) polyesters. Suitable saturated polyethers include
polymers of propylene oxide or propylene oxide/ethylene oxide. Such
materials are usually triols or diols with molecular weights between 1000
and 7000. Suitable saturated acrylics include derivatives of acrylic acid,
such as methyl methacrylate, co-polymerized with hydroxyl functional
monomers, such as 2-hydroxy-ethyl methacrylate. Polyols marketed by Miles
Corporation, Pittsburgh, Pa., under the trademark DESMOPHEN are
particularly contemplated for use herein. One such resin is Desmophen
651A-65. Several others are Desmophen 670A-80 and Desmophen 631A-75.
In addition to these polyhydroxyl compounds, other materials containing a
reactive hydrogen atom that would react with the isocyanate or
isocyanurate group to form the polyurethane can be utilized. Such
materials include polyamines, polyamides, short oil alkyds, castor oil,
epoxy resins with secondary hydroxyl groups, phenolic resins, and hydroxyl
functional vinyl resins. Suitable examples of such materials include
Ancamine 2071, a modified polyamine marketed by Pacific Anchor Chemical
Corporation, Los Angeles, Calif., EPON V-40, a polyamide marketed by Shell
Chemical Company, Houston, Tex., Aroplaz 1133-X-69, a short oil alkyd
marketed by Spencer Kellogs Products Div., Reichhold Chemicals Inc.,
Minneapolis, Minn., EPON resin 828, an epoxy resin marketed by Shell
Chemical Company, Pentalyn 802A, a phenolic modified polyester resin
Marketed by Hercules Inc., Wilmington, Del., and VAGH, a hydroxyl
functional vinyl resin marketed by Union Carbide, Danbury, Conn.
The hydroxyl functional polyol is carried in a solvent, with the solvent
solution containing from about 15 to 35% by weight of the polyol solids.
Suitable solvents for use herein include the known polyurethane solvents,
for example, butyl acetate, methyl isobutyl ketone, methyl amyl ketone,
propylene glycol monomethyl ether acetate, and mixtures thereof.
Particularly suitable as a solvent or co-solvent is methyl amyl ketone
because its high dipole constant permits a greater amount of polyol or
other resin solids to be dispersed therein. The advantages of the use of
methyl amyl ketone in top coat coating systems, as well as examples
illustrating such use, are described in U.S. Pat. No. 5,409,233 by Thomas
Kennedy, the disclosure of which is hereby incorporated by reference.
Other additives can be included in the first part of the polyurethane
system. These additives include U.V. stabilizers and absorbers, leveling
agents, optical brighteners, mar and slip agents, catalysts, antioxidants,
reactive diluents, and defoaming agents.
U.V. stabilizers function to tie up free radicals in the top coating that
are produced upon exposure to ultraviolet radiation, thus maintaining the
integrity of the coating. A suitable U.V. stabilizer is Tinuvin 292, a
hindered amine light stabilizer sold by Ciba-Geigy Corporation, Ardsley,
N.Y. U.V. absorbers function to absorb ultraviolet radiation and re-emit
it as heat. Examples of suitable U.V. absorbers for use in the present
invention are Tinuvin 1130, a benzotriazole U.V. absorber sold by
Ciba-Geigy Corporation, and Sanduvor 3206, an oxalamide derivative sold by
Clariant Corporation, Charlotte, N.C.
Suitable leveling agents which reduce the surface tension of the coating
for improved coating flow include Fluorad FC-430, a fluorochemical
surfactant sold by 3M Industrial Chemical Products Division, St. Paul,
Minn. and DOW 57, a silicone additive sold by Dow Coming Corporation,
Midland, Mich.
Optical brighteners are added to the polyurethane system so that the
coating coverage can be checked under U.V. light, as well as to brighten
the balls. Suitable optical brighteners include Uvitex OB, believed to be
2,2'-(2,5-thiophenediyl) bis (5-ter-butylbenzoxazole), sold by Ciba-Geigy
Corporation, Ardsley, N.Y., and Leucopure EGM, a coumarin optical
brightener sold by Sandoz Chemicals Corporation, Charlotte, N.C.
Catalysts are added to increase or control the rate of reaction between the
first and second parts of the polyurethane system. Catalysts contemplated
for use herein include zinc octoate, zinc octanoate, potassium octoate,
potassium acetate, and organotin compounds such as dibutyltin dilaurate,
dibutyltin diacetate, dibutyltin di(2-ethylhexanoate), stannous octanoate,
dibutyltin bis(isooctyl mercaptoacetate), dioctyltin bis(isooctyl
mercaptoacetate), dimethyltin bis(isooctyl mercaptoacetate),
bis(2-carbobutoxyethyltin) bis(isooctyl mercaptoacetate), dibutyltin
sulfide dibutyltin bis(lauryl mercaptide), dibutyltin
.beta.-mercaptopropionate dibutyltin bis(mercaptoethyldecanoate) (also
other esters), butylthiostannoic acid anhydride, butyltin
tris(isoctylmercaptoacetate), dibutyltin maleate (dioctyltin derivative),
dibutyltin bis(monoisooctylmaleate) (also other alkyl maleate esters),
stannous acetate, stannous ethylene glycoxide, stannous formate, stannous
gluconate, stannous oleate, stannous stearate, stannous tartrate, stannous
oxalate, tetrabutyltin, (CH.sub.3).sub.2 SnCl.sub.2, (C.sub.4
H.sub.9).sub.2 SnCl.sub.2, (C.sub.4 H.sub.9).sub.2 SnBr.sub.2, (C.sub.4
H.sub.9).sub.2 SnI.sub.2, (C.sub.6 H.sub.5).sub.2 SnCl.sub.2, (CH.sub.3
OC(O)CH.sub.2 CH.sub.2).sub.2 SnCl.sub.2, (CH.sub.3).sub.2 Sn(SC.sub.4
H.sub.9).sub.2, (C.sub.4 H.sub.9).sub.2 Sn(SC.sub.4 H.sub.9).sub.2,
(C.sub.4 H.sub.9).sub.2 Sn(OCH.sub.3).sub.2, CH.sub.3 SnCl.sub.3, CH.sub.3
SnBr.sub.3, C.sub.4 H.sub.9 SnCl.sub.3, C.sub.6 H.sub.5 SnCl.sub.3,
[(C.sub.4 H.sub.9).sub.2 SnS].sub.3, [C.sub.4 H.sub.9 Sn].sub.2 O,
(C.sub.4 H.sub.9).sub.3 SnF, (C.sub.4 H.sub.9).sub.3 SnOCOC.sub.6 H.sub.5,
(C.sub.4 H.sub.9).sub.3 SnOCOCH.sub.3, (C.sub.6 H.sub.5).sub.3 SnOH,
(C.sub.6 H.sub.5).sub.3 SnF, (C.sub.6 H.sub.5).sub.3 SnOCOCH.sub.3,
(C.sub.6 H.sub.11).sub.3 SnOH, (C.sub.6 H.sub.11).sub.3 SnN.sub.3 C.sub.2
H.sub.2, (Neoph.sub.3 Sn).sub.2 O, (CH.sub.3).sub.3 SnCl, (CH.sub.3).sub.3
SnBr, (C.sub.4 H.sub.9).sub.3 SnCl, (C.sub.6 H.sub.5).sub.3 SnCl, (C.sub.6
H.sub.11).sub.3 SnCl, (CH.sub.3).sub.4 Sn, (C.sub.4 H.sub.9).sub.4 Sn,
(C.sub.8 H.sub.17).sub.4 Sn, (C.sub.6 H.sub.5).sub.4 Sn, (C.sub.6
H.sub.11).sub.4 Sn, (CH.sub.2 .dbd.CH).sub.4 Sn, (CH.sub.3).sub.2 (C.sub.4
H.sub.9).sub.2 Sn, (C.sub.2 H.sub.5).sub.3 (C.sub.4 H.sub.9)Sn,
##STR1##
and
##STR2##
Any other suitable catalyst known to those skilled in the art is
contemplated for use in the inventive polyurethane system, including any
other organotin compounds described in 23 KIRK-OTHMER, ENCYCLOPEDIA OF
CHEMICAL TECHNOLOGY 52-77 (3rd ed. 1983), which is incorporated herein by
reference. Catalysts can be added to the system in any amount effective to
obtain the desired impact on the rate of reaction. Alternately, catalysts
can be added at greater than about 0.17 percent by weight of solids in the
entire polyurethane system. Several commercial catalysts, available from
Air Products and Chemicals, Inc., Allentown, Pa., are Dabco K-15 (based on
potassium octoate), Dabco T-12 (dibutyltin dilaurate), Dabco T-120, and
Polycat 46 (based on potassium acetate).
Reactive diluents are added to the polyurethane system in order to reduce
viscosity and improve flow of the components. When the polyurethane coat
is formed, the diluent reacts into the system leaving behind no residual
material that must be removed. Reactive diluents contemplated for use
herein include butyl glycidyl ether, C.sub.8 -C.sub.10 -aliphatic
monoglycidal ether, C.sub.12 -C.sub.14 -aliphatic monoglycidal ether,
cresyl glycidyl ether, neopentyl glycol diglycidyl ether, and
oxazoladine-based reactive diluents. Any other suitable reactive diluent
known to those skilled in the art is contemplated for use in the inventive
polyurethane system. Several commercial oxazoladine-based reactive
diluents, available from Angus Chemicals, Inc., Buffalo Grove, Ill., are
ZOLDINE RD-20 and ZOLDINE RD-4.
In addition to the additives, co-reactants can be incorporated into the
polyol portion of the coating system. Such co-reactants can be either
compositions that further polymerize with heat, or compositions that form
a film after the solvent is evaporated during the polyurethane
polymerization process. Such materials do not react with the isocyanate or
isocyanurate portion of the coating system, but instead act independently
to improve the final coating properties. A suitable polymerizing material
for use herein is Cymel 303, a melamine resin sold by American Cyanamid.
An example of a suitable film-forming resin is A-101, an acrylic,
non-hydroxyl containing resin sold by Rohm & Haas, Philadelphia, Pa.
The additives and co-reactants are added in amounts from about 0-20% by
weight of the total coating system. Preferably they are added in amounts
from about 1-5% by weight of the total coating system.
The second part of the polyurethane system comprises a blend of an
aliphatic diisocyanate and an aliphatic/aromatic polyisocyanate copolymer
carried in a solvent. While various aliphatic diisocyanates may be used in
the blend, excellent color retention, adhesion, and abrasion resistance in
the polyurethane top coating are achieved with a biuret or trimer of
hexamethylene diisocyanate (HDI), as described in U.S. Pat. No. 5,549,220.
The biurets and isocyanurate trimers of HDI utilized in the present
invention should have a viscosity within the range of about 3 to 10,000
cps, with the preferred range being from about 50 to 5,000 cps. Low
viscosity biuret and trimer crosslinking agents are preferred because they
allow the total coating system to have a higher solids content and still
have a viscosity that facilitates spray painting/air atomization of the
coating system on the outer surface of the golf ball. Biurets and trimers
of HDI contemplated for use herein are sold by Miles under the trademark
DESMODUR. One such composition is DESMODUR N-3200, a low viscosity biuret
of HDI. The isocyanate or isocyanurate equivalent weight of the biuret or
trimer crosslinking agent used herein should be within the range of 100 to
1,200, alternately 150 to 300.
The second component of the isocyanate blend comprises an
aliphatic/aromatic polyisocyanate copolymer. While various
aliphatic/aromatic polyisocyanate copolymers may be suitable, desirable
results are achieved with a copolymer composed of both HDI and toluene
diisocyanate (TDI). One such copolymer is sold by Miles Corporation,
Pittsburgh, Pa., under the trademark DESMODUR HL (the copolymer is
dissolved in n-butyl acetate and is sold as a clear liquid). It has been
found that the addition of such a copolymer to the second part of the
polyurethane top coat improves the drying (or curing) time of the top coat
while at the same time maintaining desirable qualities such as superior
adhesion and abrasion resistance, and good color retention upon exposure
to ultraviolet radiation. This result is unexpected because, among other
things, the copolymer blend is partly aromatic, and prior urethane
coatings made from aromatic diisocyanates tended to yellow very quickly
upon exposure to ultraviolet light. To achieve the desired results, the
aromatic/aliphatic polyisocyanate copolymer should be in the composition
at up to 50 parts by weight per 50 parts by weight of the purely aliphatic
diisocyanate. Alternately, the aromatic/aliphatic polyisocyanate copolymer
should be in the composition at up to 30 parts by weight per 70 parts by
weight of the aliphatic diisocyanate. As yet other alternatives, the
aromatic/aliphatic polyisocyanate copolymer should be in the composition
at up to 20 parts by weight per 80 parts by weight of the aliphatic
diisocyanate, or at up to 10 parts by weight per 90 parts by weight of the
aliphatic diisocyanate.
The isocyanate blend is carried in a solvent, with the solvent solution
containing from a minimum of about 40% (or less, if a quite dilute
solution is preferred for some reason), alternatively about 60%,
alternatively about 70%, to a maximum of 100%, alternatively about 85%, by
weight of the aliphatic diisocyanate and the aliphatic/aromatic
polyisocyanate copolymer. Suitable solvents for the blend include methyl
isobutyl ketone, methyl amyl ketone, butyl acetate and propylene glycol
monomethyl either acetate. The use of methyl isobutyl ketone as the
solvent or part-solvent is advantageous in that it tends to alleviate any
potential moisture problems encountered with the acetate solvents.
The first part of the polyurethane coating system containing the polyol and
other additives is mixed with the second part of the coating system
containing the isocyanate blend at an index or ratio of N.dbd.C.dbd.O to
OH in the range of 0.90 to 1.5, alternately with an index in the range of
0.95 to 1.2. An index of 1.05 may be advantageous since it takes into
account any water that may be present in the polyol, and water vapor
present in the air. The excess isocyanate insures that all of the polyol
will be polymerized, with any excess isocyanate being converted to a
polyurea. If any excess polyol is present, it will not polymerize and
tends to act as a plasticizer, thus resulting in a coating of decreased
hardness. When the two parts of the coating system are combined, the total
system has the following general formulation:
______________________________________
Polyol and isocyanate blend
35-100%
Solvent 0-65%
Additives and/or co-reactants 0-20%
______________________________________
The coating system is applied to the outer surface of the golf ball using
any conventional method. The outer surface may be either the cover of the
golf ball or, more typically, a primer coat that has been applied to the
cover of the golf ball. The cover of the golf ball is usually made of an
ionomer resin such as SURLYN (a trademark of E.I. DuPont De Nemours & Co.,
Wilmington, Del.) or IOTEK (a trademark of Exxon Chemical Co., Polymers
Group, Baytown, Tex.). The cover may, however, be made of balata (a
natural resin) or a thermoplastic polyurethane. For golf balls having a
cover made of an ionomer having a relatively high zinc content, a cover
made of thermoplastic polyurethane, or a cover made of mixtures of
ionomers and polyurethanes, a primer coat may not be necessary. Thus, the
top coat can be applied directly to the cover of the ball with good
adhesion. Also, the urethane coatings herein having a relatively high
index exhibit very good adhesion to the golf ball cover without the need
for a primer coat.
Whether the top coat is applied directly to the cover or to a primer coat,
it is preferred that the coating system be applied by spraying the coating
onto the ball. One method of spraying the coating is as follows: Using
plural spray equipment, separate streams of the polyol and the isocyanate
blend are mixed just prior to entering an air atomizing spray gun. Dry air
is used to push the coating into the spray gun where it is forced out of a
small diameter (0.1 inches) fluid nozzle. The material is then atomized at
the tip of the gun by the air cap, again using dry air. This forms a fan
of the droplets that impinge upon the surface of the golf ball. The golf
balls are then placed in a 160.degree. F. oven until the solvent
evaporates and the polyol and the isocyanates polymerize to form the
polyurethane top coat.
The inventive top coating demonstrates an increased rate of curing compared
to other top coatings having similar abrasion resistance and color
retention qualities. It is believed that the increased rate of curing can
be attributed to the aromatics present in the isocyanate copolymer,
although the inventor in no way intends to be bound by this theory.
Despite the presence of some aromatics, the inventive top coating tends to
be less subject to the yellowing that plagued early urethane coatings made
from aromatic diisocyanates. Several distinct benefits can be realized by
increasing the cure rate, and thereby reducing the heat applied to the
golf balls or the amount of time the golf balls spend in the ovens.
Because less energy is applied during the manufacturing process, the cost
of manufacturing is reduced. In addition, there is less chance that the
heating process will damage the underlying surface of the golf balls.
The invention is further illustrated, but is not intended to be limited by,
the following examples.
EXAMPLE 1
A composition in accordance with the present invention is made using the
ingredients in Table 1. Using plural spray equipment, portion "A" is mixed
with portion "B" and the mixture is immediately sprayed onto the surface
of a dozen golf balls. The golf balls are baked in an oven set at
160.degree. F. for eight minutes and then exposed to room temperature air
for approximately twenty minutes.
TABLE I
______________________________________
WEIGHT
MATERIAL WEIGHT SOLIDS
______________________________________
PART A
Polyester resin in solvent
83.62 66.90
(Desmophen 670A-80)
Polyester resin in solvent 31.86 23.89
(Desmophen 631A-75)
Methyl isobutyl ketone 33.98 0.00
Methyl amyl ketone 41.54 0.00
Leveling additive (Fluorad FC-430) 0.34 0.34
U.V. stabililzer (Tinuvin 292) 0.80 0.80
U.V. absorber (Sanduvor 3206) 0.80 0.80
Optical brightener (Uvitex OB) 0.11 0.11
Reactive diluent (Zoldine RD-20) 4.78 4.78
Catalyst (Dabco T-12) 0.32 0.32
PART B
HDI biuret (Desmodur N-3200)
57.66 57.66
Polyisocyanate copolymer 10.68 6.41
in solvent (Desmodur HL)
Methyl isobutyl ketone 15.08 0.00
Methyl amyl ketone 18.44 0.00
TOTAL (parts A and B) 300.01 162.01
Weight parts polyisocyanate copolymer per
10:90
weight parts diisocyanate (HDI biuret)
______________________________________
The quality of the top coat on the finished golf balls is assessed by aging
the golf balls in a xenon arc weatherometer and by subjecting the balls to
a "wet barrel" test. The wet barrel test is conducted by soaking a dozen
finished and cured golf balls that have been out of the oven for at least
48 hours in tap water for three hours. The balls are then shot at 125
feet/sec. against a steel wall that is at a 45 degree angle to the vector
of the golf ball. The steel wall also has vertical corrugations on it to
simulate the face of a golf club. The ball is allowed bounce around in a
barrel (hexagonal shaped) and, after reaching the bottom, is returned to
the beginning of the cycle. The test is repeated 100 times. At the end of
the test, the golf balls are dyed using a Pylam dye. This dye stains the
coating brown but leaves the ionomer cover white, thus showing areas where
the coating has worn off.
The golf balls made in accordance with Example 1 demonstrate excellent
adhesion and abrasion resistance and also good color retention
(non-yellowing) properties and yet exhibit an increased rate of curing
compared to other top coatings with similar properties. The rate of curing
is gauged by assessing the tackiness of the golf balls approximately ten
minutes after they leave the oven. The balls made in accordance with
Example 1 exhibit less tackiness (indicative of faster curing) than
similar balls covered with existing top coats having similar abrasion and
color retention qualities.
EXAMPLE 2
A composition in accordance with the present invention is made using the
ingredients in Table 2. Using plural spray equipment, portion "A" is mixed
with portion "B" and the mixture is immediately sprayed onto the surface
of a dozen golf balls. The golf balls are baked in an oven set at
160.degree. F. for eight minutes and then exposed to room temperature air
for approximately twenty minutes.
TABLE 2
______________________________________
WEIGHT
MATERIAL WEIGHT SOLIDS
______________________________________
PART A
Polyester resin in solvent
83.34 65.87
(Desmophen 670A-80)
Polyester resin in solvent 31.37 23.53
(Desmophen 631A-75)
Methyl isobutyl ketone 34.13 0.00
Methyl amyl ketone 41.72 0.00
Leveling additive (Fluorad FC-430) 0.34 0.34
U.V. stabililzer (Tinuvin 292) 0.80 0.80
U.V. absorber (Sanduvor 3206) 0.80 0.80
Optical brightener (Uvitex OB) 0.11 0.11
Reactive diluent (Zoldine RD-20) 4.71 4.71
Catalyst (Dabco T-12) 0.32 0.32
PART B
HDI biuret (Desmodur N-3200)
46.51 46.51
Polyisocyanate copolymer 33.22 19.93
in solvent (Desmodur HL)
Methyl isobutyl ketone 11.05 0.00
Methyl amyl ketone 13.50 0.00
TOTAL (parts A and B) 300.92 162.92
Weight parts polyisocyanate copolymer per
30:70
weight parts diisocyanate (HDI biuret)
______________________________________
The quality of the top coat on the finished golf balls is assessed by aging
the golf balls in a xenon arc weatherometer and by subjecting the balls to
a "wet barrel" test. The golf balls made in accordance with Example 2
demonstrate excellent adhesion and abrasion resistance and also good color
retention (non-yellowing) properties and yet exhibit an increased rate of
curing compared to other top coatings with similar properties.
Specifically, the balls made in accordance with Example 2 are tack-free
when tackiness is assessed approximately ten minutes after the balls leave
the oven.
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